1. Field of the Art
The present invention relates to a method of and apparatus for generating a low-energy neutral particle beam. More particularly, the present invention relates to a method and apparatus capable of generating a low-energy neutral particle beam which has a large diameter, low energy and a velocity higher than thermal velocity and in which neutral particles are uniform in direction.
2. Prior Art
There has heretofore been proposed a neutral particle beam generating technique wherein a saddle electric field is formed by using DC electric discharge, and a gas is ionized to produce ions by using the oscillation of electrons in the electric field, thereby generating a neutral particle beam through charge exchange and recombination with electrons. Such a neutral particle beam generating technique is, for example, shown in Japanese Patent Public Disclosure No. 183900/86. There has also been developed a neutral particle beam generating apparatus capable of raising the discharge efficiency and sustaining the electric discharge at low gas pressure by using PIG (Penning Ionization Gauge) electric discharge.
However, the above-described conventional neutral particle beam generating technique and apparatus suffer from various problems. For example, the discharge sustaining voltage is relatively high, so that the interior of a neutral particle beam source and a container may be contaminated by sputtering of an electrode constituting material. As the discharge voltage is lowered, the neutral particle beam density decreases and therefore, when it is intended to generate a neutral particle beam having a large diameter, the electric discharge becomes unstable.
There is also a method of forming a neutral particle beam by letting out heated gas molecules from a nozzle unlike the above-described neutral particle beam generating technique and apparatus. However, this method has disadvantages in that since gas molecules are heated, reaction of the furnace material with the gas molecules gives rise to a serious problem, and that it is difficult to obtain a neutral particle beam having a large diameter.
Further, a neutral particle beam generating apparatus using ECR (electron cyclotron resonance) electric discharge that utilizes resonance of a microwave and a magnetic field has recently been proposed. This apparatus suffers, however, from some problems. Namely since ECR electric discharge requires a high magnetic field intensity, the apparatus becomes large in size. Further, it is necessary in order to produce a uniform plasma to dispose a plurality of magnetic fields. As a result, the apparatus becomes complicated.